This invention relates to a spirit level which is easily adjusted to true horizontal using a known level surface. The inventive apparatus also comprises a rotatable spirit level adjustable to any desired angle relative to the horizontal, such that a surface may be aligned at the predetermined angle. In a preferred embodiment. The device comprises a plurality of bubble vials; one parallel to a flat contact surface of the device, one perpendicular to the contact surface and a third rotatably adjustable and calibrated between 0 and 90 degrees for angular measurement.
Adjustable spirit levels are well-known in the prior art. U.S. Pat. No. 716,001, issued Dec. 16, 1902, discloses a spirit level having multiple vials, rotatably adjustable by loosening threaded cylinders containing the vials. U.S. Pat. No. 1,133,936, issued Mar. 30, 1915, discloses a level utilizing a rotatably adjustable vial that was held within a toothed circular disc that allowing coarse adjustment by rotating and then clamping the disc, and vernier adjustment by a second rotatable internal disc. U.S. Pat. No. 1,264,161, issued Apr. 30, 1918, disclosed a combination square, spirit level and protractor having a calibrated and rotationally adjustable spirit level for use in measuring or laying out angled surfaces. U.S. Pat. No. 2,993,281, issued July 25, 1961, discloses a combination spirit level and protractor wherein the level can be rotated and in any angularly position by loosening a plurality of fasteners. U.S. Pat. No. 4,774,767, issued Oct. 4, 1988, discloses an angularly adjustable spirit level which can be secured in a desired position by a clamping jaw.
Carpenters and electricians have experienced two primary problems with available levels: firstly, the levels are manufactured with inexact tolerances that produce variability which is unacceptable in many construction trades, and secondly, the levels are not adjustable so as to permit either correction of the manufacturing inaccuracies or measurement of precise angles other than vertical or horizontal.
It is the purpose of this invention to provide adjustability to a fixed spirit level and to provide simple adjustability to a calibrated rotatable spirit level, such that the rotatable position can be securely fixed once adjusted.